Note: Descriptions are shown in the official language in which they were submitted.
10~'3S34
11279
Field of the Invention
The invention relates to non-aqueous lead
oxide cells, and specifically to such cells wherein
the positive electrode comprises lead dioxide particles
having an outer layer of lead monoxide.
Back~round of the Invention
The development of high energy cell systems
requires the compatibility of an electrolyte possessing
desirable electrochemical properties with highly active
anode materials, such as lithium, calcium, sodium and
the like, and the efficient use of high energy density
cathode materials, such as FeS2, Co304, PbO2 and the
like. The use of aqueous electrolytes is precluded
in these systems since the anode materials are suffi- -
ciently active to react with water chemically. There-
fore, in order to realize the high energy density
obtainable through use of these highly reactive anodes
and high energy density cathodes, it is necessary to
use a non-aqueous electrolyte system.
One of the major disadvantages of employing
lead dioxide as the active cathode material in a non-
aqueous electrolyte system is that it will discharge
at two different potentials. The first step in the
discharge curve is attributed to the reduction of the
lead dioxide to lead monoxide, while the second step
is attributed to the reduction of the reaction product, ~ ~
lead monoxide. Contrary to lead dioxide, lead monoxide
",.... - .. . . . - .
. . .................................. .. .. . . .... .
.~ . , .: . . . . . .
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11279
will discharge in a non-aqueous cell system at a uni-
potential level. One advantage in employing lead
dioxide as the cathode material over lead monoxide is
that it has almost double the capacity of lead monoxide,
Thus in a non-aqueous electrolyte system, lead monoxide
will have the advantagP of discharging at a unipotential
plateau with the disadvantage of having a relatively
low capacity while lead dioxide will have the advantage
of having a relatively high capacity with the disad-
vantage of discharging at two distinct voltage plateaus.
Many cell or battery applications, particularly
in transistorized devices such as hearing aids, watches
and the like, require a substantial unipotential dis-
charge source for proper operation and, therefore,
cannot use the dual voltage level discharge which is
characteristic of non-aqueous lead dioxide cells.
This du~l voltage level discharge characteristic is
similar to the dual voltage discharge characteristic
of aqueous alkaline divalent silver oxide cells.
Although many approaches have been proposed for obtain-
ing a unipotential discharge from an aqueous alkaline
divalent silver oxide cell, the approaches are not
needed when lead dioxide is employed in an aqueous
electrolyte cell system. Specifically, in an aqueous
electrolyte cell system, lead dioxide will discharge
almost entirely at its higher voltage level so that,
in effect, the cell will produce a substantially
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11279
unipotential discharge over the useful life of the
cell. Contrary to this, when lead dioxide is used
as the cathode material in a non-aqueous electrolyte
system, the cell will discharge at a first potential
for a significant time period and then decrease to a
distinct lower potential for the remainder of the
discharge, A problem usually encountered in various
cell systems is that although an electrode-couple can
function in an aqueous electrolyte, it is practically
impossible to predict in advance how well, if at all,
it will function in a non-aqueous electrolyte. Thus
a cell must be considered as a unit having three
parts - a cathode, an anode and an electrolyte - and
it i9 to be understood that the parts of one cell may
not be predictably interchangeable with parts of
another cell to produce an efficient and workable cell.
A French Patent 2,288,401 published on
June 18, 1976 (counterpart to German application
2,545,498 published on April 27, 1976~ discloses a non-
aqueous cell which employs a negative electrode, such
as lithium, a non-aqueous-solvent electrolyte and a
positive active electrode consisting of a positive active
~aterial of the oxides and oxidizing salts, the dis-
charged reduction of which leads to metals of the group
including lead, tin, gold, bismuth, zinc, cadmium and
their alloys and an electronic conductor consisting ~
at least on ~he surface of a material selected -
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lU~ 34 11279
from the group including lead, tin, gold, bismuth, zinc,
cadmium and their alloys. Several examples are disclosed
in this reference in which lead monoxide is employed as the
positive active material and lead, tin or graphite is
employed as the electronic conductor. Although this
reference teaches one means for obtaining a unipotential
discharge for certain non-aqueous cell systems, as, for
example, a cell employing lead monoxide as the positive
active material, the subject invention is directed to
the use of lead dioxide particles having a lead monoxide
outer layer as the positive active material of a non-
aqueous cell. The positive active material of this in-
vention could also be expressed as lead monoxide particles
having a lead dioxide core.
Accordingly, it is the primary object of this
invention to provide a non-aqueous lead oxide cell which
employs a positive electrode comprising lead dioxide
particles each having a lead monoxide outer layer, and
which has a substantially unipotential discharge
voltage.
Another object of this invention is to provide
a non-aqueous lead oxide cell which employs a lithium
anode and a positive cathode composed of lead dioxide
particles each having a lead monoxide outer layer, and
which has a substantially unipotential discharge
voltage.
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11279
Another object of this invention is to provide
a non-aqueous lead oxide cell which employs a positive
electrode composed of lead dioxide particles each having
a lead monoxide outer layer, and wherein said lead
monoxide varies between about 1 per cent and 60 per cent
by weight of the lead oxides.
Summarv o~ the Invention
The invention relates to a non-aqueous lead
oxide cell comprising a highly active metal negative
electrode, a positive electrode and a non-aqueous elec-
trolyte; said positive electrode comprising lead dioxide
particles each having a substantially complete outer
layer of lead monoxide, and said cell having a sub-
stantially unipotential discharge voltage. ~ ~
A unipotential discharge voltage shall mean ~ -
a relatively constant voltage level extending over at
least 85 per cent of a cell's discharge capacity when
discharged across a fixed load, and wherein the voltage
varies no more than + 10 per cent of the average ~oltage
of said voltage level. For example, a unipotential dis-
charge level can be represented by a voltage-time curve
substantially free from voltage excursions or steps
during at least 85 per cent of the time of discharge
across a constant load, such steps or excursions being
defined as voltage readings outside of + 10 per cent of
the average voltage over the said 85 per cent portion ~ -
of the time of discharge. As shown in Figure 1, it is
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11279
the object of this invention to effectively eliminate
or effectively suppress the portion of the curve to
the leEt of point A to yield a unipoten~ial discharge
level as generally shown by the curve between points
A and B.
It is also within the scope of this invention to
add a binder, an electronically conductive material, an
electrolyte-absorbent material or mixtures thereof to
the positive electrode of this invention.
The size of the lead monoxide~coated lead
dioxide particles comprising the cathode of this invention
should preferably be between about 0.04 mm and about
0.47 mm and more preferably between about 0.07 mm and
about 0.23 mm. Particles sized smaller than about 0.04
mm will provide a large true surface area but, however,
when fabricated into a cathode, the electronic conductivity
of the cathode will generally be insufficient for
commercial cell application due to the large number of
particle-to-particle contacts providing the conductive
path through the cathode to the cathode collector of
the cell. A cathode fabricated with lead monoxide-coated
lead dioxide particles sized larger than about 0.47 mm
will have a small true surface area which will generally
not support a current density generally required for
cu~ercial cell application.
The per cent by weight of lead monoxide in
the lead dioxide-containing positive electrode of this
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9 5 3~
11279
invention should be between about 1 per cent and about
60 per cent based on the weight of the lead oxldes and
preferably between about 10 per cent and about 40
per cent based on the weight of the lead oxides, A
lead monoxide amount less than about 1 per cent by weight
of the lead dioxides would be insufficient to reliably
and substantially eliminate the two voltage plateau
discharge characteristic of lead dioxide in a non-aqueous
electrolyte cell system. An amount of lead monoxide
greater than about 60 per cent by weight of the lead;~
oxides would be inefficient since too ~uch of the high
capacity lead dioxide material would be replaced by the
lower capacity lead monoxide material.
Useful highly active negative anode materials
are generally consumable metals and include aluminum,
the alkali metals, alkaline earth metals and alloys of
alkali metals or alkaline earth metals with each other
and other metals. The term "alloy" as used herein and
in the appended claims is intended to include mixtures,
solid solutions, such as lithium-magnesium, and inter-;~
metallic compounds, such as llthium monoaluminide.
The preferred anode ma~erials are lithium, sodium,
potassium, calcium, and alloys thereof. ~;
Useful organic solvents employed alone or
mixed with one or more other solvents for use in this ;
invention include the following classes of
compounds:
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S34
11279
Alkylene nit riles: e.g., cro t onitrile
(li~uid range -51.1C. to 120C.)
Trialkyl borates: e.g., trimethyl borate, (CH30)3B
(liquid range -29 3 to 67C.)
Tetraalkyl silicates: e.g , tetramethyl silicate,
(CH30)4Si (boiling po~nt 121C.)
Nitroalkanes- e g., nitromethane, CH3N02
(li~uid range -17 to 100.8C.)
Alkylnitriles: e.g., acetonitrile, CH3CN
(li~uid range -45 to 81.6C.)
D~alkylamides: e.g , dimethylformamide, HCON(CH3)2
(liquid range -60;48 to 149C.)
Lactams: e.g " N-methylpyrro~idone,
H2-CH2-CH2-CO-N-CH3 (l~quid range -16 to 202C,)
Tetraalkylureas: e g., tetramethylurea,
(CH3)2N-CO-NtCH3)2 (ll~uid range -1.2 to 166C.)
Monocarboxylic acid esters: e.g., ethyl acetate
(liquid range -83.6 to 77.06C.) -
Orthoesters: e,g" trimethylorthoformate, HC(OCH3)3
~bo~ling point 103C.)
-
Lactones: e.g., ~r~amma)butyrolactone, CH2 CH2-CH2-0-CO
(li~uid ran~e -42 to 206C.)
D~alkyl carbonates: e.g., dimethyl carbonate,
OC(OCH3)2 (liquid range 2 to 90C.)
Alkylene carbonates: e,g., propylene carbonate,
CH(CH3)CH2-0-CO-0 (liquid range -48 to 242C,) ~
Monoethers: e.g., diethyl ether (liquid range -116 ~ -
to 34.5C.)
9S 3 ~
11279
Polyethers: e.g., 1,1- and 1~2-~dimethoxyethane
(liquid ranges -113.2 to 64,5C. and -58 to
83C., respectively)
Cyclic ethers: e g., tetra~ydrofuran (liquid range
-65 to 67C.); l,3-dioxolane (llquid range
-95 to 78C.)
Nitroaromatics: e.g., nitrobenzene (liquid range
5.7 to 210.8C.)
Aromatic carboxylic acid halides: e.g., benzoyl
chloride (liquid range 0 to 197C.); benzoyl
bromide (liquid range _~6 to 218C.)
Aromatic sulfonic acid halides- e.g., benzene sulfonyl
chloride (liquid range 14.5 to 251C )
Aromatic phosphonic acid dihalides: e.g., benzene
phosphonyl dichloride (boiling point 258~C )
Aromatic th~ophosphonic acid dihalides: e,g.,
benzene thiophosphonyl dlchloride (boiling
point 124C. at S mm.) ;
Cyclic sulfones: e.g., sulfo~ane,
CH2'C~2-CH2-CH2-S2 (melting point 22C );
3-methylsulfolane (melting point -1C.) ~
Alkyl sulfonic acid halides: e,g., methanesulfonyl ~ -
chloride (boiling point 161C.) -
Al~yl carboxylic acid halides: e.g,, acetyl chloride
~ (liquid range -112 to 50.9C.); acetyl br~mide
(liquid range -96 to 76.C.~; propionyl
chloride (liquid range ~94 to 8Q~
10 ~
10~9~3~
11279
Saturated heterocyclics: e.g., tetrahydrothiophene
(liquid range -96 to 121C.); 3-methyl-2-oxa-
zolidone (~elting po~nt 15,9C.)
Dialkyl sulfamic scid halides: e.g., d~methyl
sulfamyl chloride (boiling point 80C, at 16 mm.)
Alkyl halosulfonates: e.g., ethyl chlorosulfonate
(boiling point 151C.)
Unsaturated heterocyclic carboxylic acid halides:
e.g., 2-furoyl chloride (liquid range -2 to 173C.)
Five-membered unsaturated heteroc~clics: e.g.,
3,5-dimethylisoxazole (boillng po~nt 140C.);
l-methylpyrrole (boiling point 114C.);
2,4-dimethylthia201e (boiling point 144C.);
furan (liquid range -85.65 to 31,36C.) -
Este~s andlor halides of dibàsic carboxylic acids:
e.g., ethyl oxalyl chloride (boiling point 135C.)
Mixed alkyl sulfonic acid halides and carboxylic
acid halides: e.g., chlorosulfonyl acetyl
chloride (boiling point 98C. at 10 mm.)
0 Dialkyl sulfoxides: e.g., dimethyl sulfoxide (liquid
range 18.4 to 189C.)
Dialkyl sulfates: e.g., dimethylsulfate (liquid
range -31.75 to 188.5C.)
Dialkyl sulfites: e.g., dimethylsulfite (boiling -
point 126C.)
Alkylene sulfites: e.g., ethylene glycol sulfite
- (liquid range -11 to 173C.)
-- 10~9~34
11279
Halogenated alkanes: e.g., methylene chloride
(liquid range -95 to 40C:.); 1,3-dichloro-
propane ~liquid range -99.5 to 120.4C.)
Of the above, the preferred solvents are
sulfolane; crotonitrile; nitrobenzene; tetrahydrofuran;
1,3-dioxolane; 3-methyl-2-oxazolidone; propylene car-
bonate; ~ -butyrolactone; ethylene glycol sulfite;
dimethylsulfite; dimethyl sulfoxide; and 1,1- and 1,2-
dimethoxyethane. Of the preferred solvents, the best
are sulfolane; 3-methyl-2-oxazolidone; propylene car- -
bonate, 1,3-dioxolane and dimethoxyethane because they ap-
pear more chemically inert to battery components and
have wide liquid ranges, and especially because they ;~
permit highly efficient utilization of the cathode -~
materials. `
The ionizing solute for use in the invention
may be a simple or double salt, or mixtures thereof,
- which will produce an ionically conductive solution
when dissolved in one or more solvents. Preferred
solutes are complexes of inorganic or organic Lewis
acids and inorganic ionizable salts. The only require~
ments for utility are that the salts, whether simple ;
or complex, be compatible with the solvent or solvents
being employed and that they yield a solution which
is sufficiently ionically conductive. According to the ~
Lewis or electronic concept of acids and bases, many -
substances which contain no active hydrogen can act as ~ ~
12. -
- . , - :. . ,
: - . .: ;.. . ~ - :-
-
9~ 4
11279
acids or acceptors of electron doublets. The basicconcept is set forth in the chemical literature
(Journal of the Franklin Institute, Vol. 226 - July/
December 1938, pages 293-313 by Lewis).
A suggested reaction mechanism for the manner
in which these complexes function in a solvent is
described in detail in U. S. Patent No. 3,542,602
wherein it is suggested that the complex or double salt
formed between the Lewis acid and the ionizable salt
yields an entity which is more stable than either of
the components alone.
Typical Lewis acids suitable for use in the
present invention include aluminum fluoride, aluminum
bromide, aluminum chloride, antimony pentachloride,
zirconium tetrachloride, phosphorus pentachloride,
boron fluoride, boron chloride and boron bromide.
Ionizable salts useful in combination with
the Lewis acids include lithium fluoride, lithium
chloride, lithium bromide, lithium sulfide, sodium
fluoride, sodium chloride, sodium bromide, potassium -
fluoride, potassium chloride and potassium bromide.
It will be obvious to those skilled in the
art that the double salts formed by a Lewis acid and an
inorganic ionizable salt may be used as such or the
individual components may be added to the solvent
separately to form the double salt or the resulting ions
in situ. One such double salt, for example, is that
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11279
formed by the combination of alu~inum chloride and
lithium chloride to yield lithium aluminum tetrachloride.
Brief Description o~ the Drawin~s
Figure 1 is a curve showing the discharge
characteristics of a non-aqueous lead oxide-lithium
cell employing a lead dioxide positive electrode (cathode).
Figure 2 is a curve showing the discharge
characteristics of a non-a~ueous lead oxide-lithium cell
employing a lead monoxide positive electrode.
Figure 3 is a curve showing the discharge
characteristics of a non-aqueous lead oxide-lithium ~`
cell employing a positive electrode composed of lead
monoxide-coated lead dioxide particles in accordance
with the present invention.
Figure 4 is a curve showing the discharge
characteristics of a non-aqueous lead oxide-lithium
-cell employing a positive electrode composed of lead
dioxide particles and an electrolyte containing hydrazine
for surface reduction of the lead dioxide particles in
accordance with the present invention.
EXAMPLE I
A flat-type cell was constructed utilizing a
nickel metal base having therein a l-inch diameter ~!
shallow depression into which the cell contents were
placed and over which a nickel metal cap was placed
to close the cell. The contents of the cell consisted
of five sheets of lithium foil having a total thickness
1~;)89534
11279
of 0.10 inch, about 4 ml of an electrolyte, two porous
nonwoven polypropylene separator~ (0.005 ~nch thick
each) which absorbed some of the electrolyte, and a
lead dioxide cathode mix.
The electrolyte was a lM LiC104 in 77 volume
per cent dioxolane, 23 volume per cent dimethoxyethane
(DME) with a trace of about 0.1 volume per cent dimethyl
isoxazole (DMI) as a polymerization inhibitor. The
cathode was a pressed layer of 4.3 grams of lead
dioxide.
The cell was discharged across a constant load
at a 3-milliampere drain and the voltage observed
as a function of time is shown plotted as the curve on
the graph in Figure 1. Also observed and as recorded
on Figure 1 is the open circuit voltage of the cell
which wa~ 3.5 volts. As is apparent from the curve in
Figure 1, it took approximately four days before the
voltage decreased to a substantially unipotential level
of approximately 1.2 volts. As stated above, many cell and
battery operated devices which require an essentially uni-
potential power source could not use this type of cell
system because of its significant dual voltage level
discharge characteristic.
EXAMPLE II
A flat-type cell was constructed using the -~
same components as described in Example I except that
the cathode mix was a compressed layer of a mixture of
15. ~ :
lV8~53~
112 79
3 grams of lead monoxide and 0.5 gram of carbon black
added for conductivity. As in Example I, the cathode
mix was placed into the shallow depression in a nickel
metal base along with other cell componentsO ~;
The cell was discharged on a 3-milliampere
drain and the voltage observed as a function of time
is shown plotted as the curve on the graph in Figure 2.
Also observed and as recorded on Figure 2 is the open
circuit voltage of the cell which was about 3.2 volts.
This high open circuit voltage for the cell is believed
to be due to the presence of oxygen and/or oxide~ on
the surface of the carbon black in the cathode mix.
As is apparent from the curve in Figure 2,
the substantially unipotential voltage level output of
this cell makes it an admirable candidate as a power source
for many cell and battery operated devices. As stated
above, however, although this type of cell has the
advantage of discharging at a substantially unipotential
level, it has the disadvantage of having a rather low
capacity as comparet to a cell employing lead dioxide
as the cathode material.
EXAMPLE III
A flat-type cell was constructed using the
same components as described in Example I except that
the cathode was composed of lead monoxide-coated lead
dioxide particles which were prepared in the following
manner:
16.
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1089534
11279
6 grams of reagent grade PbO2 were mixed with
900 milliliters of an aqueous 0.0015 M hydrazine (N2H4)
solution and stirred for one-half hour. The mixture
was then filtered and t~e treated PbO2 was dried over-
night in a vacuum oven at approximately 82C. This
reduced the PbO2 capacity by about 30% producing lead
monoxide coated lead dioxide particles. Two grams of
the partially reduced PbO2 particles were placed into
the shallow depression in a nickel metal base along
with the other cell components as described in Example I.
To vary the reduction of PbO2 capacity all that is
necessary is to vary the amount and/or concentration
of the hydrazine solution and, if desired, the time
and/or temperature of the reaction.
The cell so produced in accordance with this
invention was then discharged across a lK-ohm load
- (about 1.2-milliampere drain) and the voltage observed
as a function of time is shown plotted as the curve on
the graph in Figure 3. Also observed and as recorded
on Figure 3 is the open circuit voltage of the cell
which was about 2.95 voltsO
As is apparent from the curve in Figure 3,
the output voltage of the cell discharged at a substan-
tially unipotential level almost immediately, even at
this lower current train, and then continued at the
lead monoxide-lithium voltage level for more than 11
days. Thus using the teachings of this invention, a
17.
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11279
non-aqueous lead dioxide cell can be made which takes
advantage of the high capacity characteristic of lead
dioxide while simultaneously effectively eliminating
the disadvantage of the dual voltage level output charac-
teristic of lead dioxide in a non-aqueous cell system.
EXAMPLE IV
A flat-type cell wa~ constructed using the
same components as described in Example I except that
the cathode was composed of 1.5 grams of lead tioxide
particles sized between 0.07 mm and 0.15 mm and the
electrolyte was lM LiCF3S03 and 0.5M hydrazine in 40
volume per cent dioxolane, 30 volume per cent dimethoxy-
ethane and 30 volume per cent 3-methyl-2-oxazolidone.
As in Example III, the surface of the lead dioxide
particles contacted by the hydrazine was reduced thereby -
forming a lead monoxide layer on said particles.
The cell so produced in accordance with this
invention was then discharged across a 2.4K-ohm load -
(about 0.6 milliampere drain) and the voltage observed
as a function of time is shown plotted as the curve on
the graph in Figure 4. Also observed and as recorded
on Figure 4 is the open circuit voltage of the cell
which was about 2.7 volts.
The curve in Figure 4 shows that the cell dis-
charged at a substantially unipotential level after
about two tays at this very low drain and then continued
at the lead monoxide-lithium voltage level until the
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10~9~34
11279
cathode was exhausted after the seventh day. Although
the test results of the cell using this method of
reducing PbO2 were not as good as the test results
of the cell using the method disclosed in Example III,
the disclosed method does demonstrate that lt can be
employed to make a non-aqueous lead dioxide cell which
takes advantage of the high capacity characteristic
of lead dioxide while simultaneously effectively elim-
inating the disadvantage of the dual voltage level
output characteristic of lead dioxide in a non-aqueous
cell system.
It is to be understood that other modifications
and changes to the preferred embodiments of the invention J
herein shown and described can also be made without
~: departing from the spirit and scope of the invention.
' . '' ~' ~
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19. ,~.
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